Renal hydatid disease: A rare case

A 69-year-old woman with an unremarkable medical history sought medical attention due to urinary urgency and right flank pain. Upon physical examination, the patient was afebrile, and palpable fullness was noted in the right upper quadrant of the abdomen and right flank, without associated tenderness.

Mildly elevated direct bilirubin, along with elevated SGOT (serum glutamic oxaloacetic transaminase) and SGPT (serum glutamic pyruvic transaminase), in addition to increased alkaline phosphatase levels noted. In further investigation, serum IgG for echinococcus was seen raised.

The MRCP examination revealed intriguing findings in the abdominal region. In the right lobe of the liver, specifically in segment VIII, a cystic lesion displaying T2 heterogeneous hyperintensity was identified. This lesion exhibits mild peripheral diffusion restriction, extending up to the subcapsular location, raising suspicion for the possibility of hydatid disease.

Further noteworthy observations were made in the right kidney, where a well-marginated unilocular endo-exophytic cystic lesion with mixed internal intensities and ill-defined membranes was noted at the lower pole. This renal lesion is situated posteriorly and medially, abutting the right psoas muscle, with preserved fat planes.

Contrary to expectations, on PET CECT, neither the liver lesion nor the renal lesion demonstrated FDG avidity. Additionally, the renal lesion displayed peripheral wall calcification, further characterizing its nature. These comprehensive imaging findings provide valuable insights for clinical correlation and potential management strategies.

Hydatid disease, a zoonosis with a global presence, is instigated by the larvae of Echinococcus tapeworms, predominantly Echinococcus granulosus [1]. Dogs are the definitive hosts for Echinococcus granulosus, while sheep serve as definitive hosts. Humans, as accidental hosts, can develop hydatid disease if they ingest tapeworm eggs [2]. Hydatid disease predominantly affects the liver (75% of cases) and the lungs (15% of cases), although it can potentially involve any organ. Renal involvement is uncommon, occurring in only 2%–3% of cases [3].

On T2-weighted MR images, hydatid cysts typically exhibit a low-signal-intensity rim, which is likely associated with the dense, fibrous pericyst [4]. Type 1 lesions present as hypointense on T1-weighted images and markedly hyperintense on T2-weighted images, resembling the imaging characteristics of simple cysts. In type 2 cysts, the maternal matrix is typically hypointense on T1-weighted images and hyperintense on T2-weighted images. The signal intensity of the daughter cysts' contents mirrors that of fluid on both T1- and T2-weighted images, with variations depending on the contents of the maternal matrix. Collapsed membranes within the daughter cysts may manifest as linear intracystic structures with low signal intensity on all MR images, irrespective of the pulse sequence. These collapsed membranes, along with the parent cyst wall, may exhibit enhancement following the administration of contrast material. Type 3 cysts, conversely, demonstrate low signal intensity on all MR images, regardless of the pulse sequence employed.

Indeed, in the context of hydatid disease, it is notable that FDG (fluorodeoxyglucose) uptake is typically not observed on imaging studies. This lack of FDG avidity, as seen in PET scans, can be a valuable characteristic in distinguishing hydatid cysts from other pathologies. The absence of increased FDG uptake is consistent with the slow metabolic activity of the cystic content, contributing to the overall imaging profile of hydatid disease [5].

Conclusion

In summary, the presence of imaging features like floating membranes, daughter cysts, and the rim sign is highly indicative of hydatid disease. Accurate diagnosis is often straightforward for a renal hydatid cyst displaying these characteristics. However, cases with a nonspecific heterogeneous appearance present a diagnostic challenge. In such instances, support for the diagnosis can be derived from the identification of hydatid cysts in other organs. The crucial role of a radiologist's proficiency in recognizing these imaging features cannot be overstated, as it is pivotal for early diagnosis and optimal treatment selection.